1. Field of the Invention
The subject invention relates to optics, illumination systems, electrooptical, light modulating and light gating systems, optical systems for converting a spatially concentrated light output into a band of light, to electro-optical systems for modulating a light output, light gate utilization methods and apparatus, methods and apparatus for recording varying electrical signals and methods and apparatus for reading information with the aid of light gates. Examples of such apparatus include solid state oscillographs and solid state facsimile equipment.
2. Disclosure Statement
This disclosure statement is made pursuant to the duty of disclosure imposed by law and formulated in 37 CFR 1.56(a). No representation is hereby made that information thus disclosed in fact constitutes prior art inasmuch as 37 CFR 1.56(a) relies on a materiality concept which depends on uncertain and inevitably subjective elements of substantial likelihood and reasonableness, and inasmuch as a growing attitude appears to require citation of material which might lead to a discovery of pertinent material though not necessarily being of itself pertinent. Also, the following comments contain conclusions and observations which have only been drawn or become apparent after conception of the subject invention or which contrast the subject invention or its merits against the background of developments subsequent in time or priority.
A review of the development of electrooptical light gate systems in light modulators and other equipment may be had from U.S. Pat. Nos. 2,591,701, 3,027,806, 3,322,485, 3,354,465, 3,454,771, 3,464,762, 3,471,863, 3,492,492, 3,499,702, 3,499,704, 3,512,864, 3,567,847, 3,582,957, 3,597,044, 3,612,656, 3,624,597, 3,644,017, 3,657,471, 3,657,707, 3,666,666, 3,699,242, 3,702,724, 3,718,723, 3,737,211, 3,781,783, 3,787,111, 3,799,647, 3,823,998, 3,867,571, 3,914,546, 3,922,485, 3,926,520, 3,930,119, 3,944,323 and 3,945,715. For information on electrooptical oscillographs and facsimile equipment, reference may also be had to German Pat. Nos. 357 299, issued Aug. 19, 1922, 492 331, issued Mar. 5, 1930 and 584 384, issued Sept. 19, 1933 and to German Published patent applications Nos. 2 321 870, published Nov. 7, 1974 and 2 322 473, published Nov. 21, 1974.
While the familiar Kerr cell naturally has spawned a multitude of proposals built on the light modulating capability of that cell, a more recent impetus in that direction has emanated from the advent of suitable light-modulating solid state materials as may be seen from U.S. Pat. Nos. 2,892,955, 2,911,370, 2,985,700, 3,144,411, 3,283,044, 3,303,133, 3,344,073, 3,429,818, 3,434,122, 3,464,924, 3,517,093, 3,531,182, 3,532,628, 3,536,625, 3,622,226, 3,630,597, 3,684,714, 3,699,044, 3,708,438, 3,728,263, 3,732,117, 3,744,875, 3,816,750, 3,826,865, 3,856,693, 3,871,745, 3,903,358, 3,917,780, 3,923,675, 3,932,313, 3,938,878 and 3,963,630 and U.S. Published patent application No. B 384,225, dated Mar. 16, 1976.
A family of ferroelectric electrooptic ceramics is known as PZT compounds with P standing for lead, Z for zirconium and T for titanium. Under the influence of an electrical field, PZT compounds become birefringent and exhibit various electrooptic properties. For instance, incoming light is resolved into two component waves propagating at different velocities and in polarization planes that are at right angles to each other. The magnitude of the effect is a function of the applied voltage and of the light frequency. Light valves and gates may be provided by placing the electrooptic ceramic between a polarizer plate and an analyzer plate.
A breakthrough occurred with the discovery that substitution of small amounts of lanthanum greatly improves ferroelectric properties. These improved compounds generally have become known as PLZT compounds, with the L standing for lanthanum.
Reference may in this respect be had to Land et al., Ferroelectric Ceramic Electrooptic Materials and Devices, 57 Proceedings IEEE No. 5, May 1969, pp. 751 to 768, Thacher et al., Ferroelectric Electrooptic Ceramics with Reduced Scattering, ED-16, IEEE Transactions on Electron Devices, No. 6, June 1969, pp. 515 to 521, Maldonado et al., Ferroelectric Ceramic Light Gates Operated in a Voltage-Controlled Mode, ED-17, IEEE Transactions on Electron Devices, No. 2, Feb. 1970, pp. 148 to 157, New Ferroelectric Ceramics Enhance Electro-Optic Performance, Design News, June 22, 1970, pp. 10 and 11, Haertling et al., Hot-Pressed (Pb, La) (Zr, Ti) O.sub.3 Ferroelectric Ceramics for Electrooptic Applications, 54 Journal of the American Ceramic Society, No. 1, Jan. 1971, pp. 1 to 11, Waterworth et al., Integrated Electro-Optic Modulator Arrays, 4 Optoelectronics (1972) 339 and 340, Cutchen et al., Electrooptic Devices Utilizing Quadratic PLZT Ceramic Elements, 30, 1973 Wescon Technical Papers, Vol. 17 pp. 1 to 12, Zook, Light Beam Deflector Performance: a Comparative Analysis, 13 APPLIED OPTICS, No. 4, Apr. 1974, pp. 875 et seq., Fiber Display Features Digital Scanning, Optical Spectra, June 1974, and Cutchen et al., PLZT Electrooptic Shutters: Applications, 14 APPLIED OPTICS, No. 8, Aug. 1975, pp. 1866 to 1873.
In the course of such development, Kerr cells in such applications as constant-density trace oscillographs disclosed in U.S. Pat. No. 3,354,465 by Merritt et al., issued Nov. 21, 1967, were replaced by solid-state light valves. Indeed, solid-state shutter systems were among the first practical applications as may, for instance, be seen from U.S. Pat. No. 3,555,987, by Iben Browning, issued Jan. 19, 1971. The switching properties and modes of ferroelectric ceramic plates were recognized and published such as in the above mentioned 1969 IEEE article by Land et al., pp. 61 and 762 and FIG. 20, and proposals for practical applications such as those suggested in the above mentioned U.S. Pat. No. 3,930,119, by Schmidt et al., issued Dec. 30, 1975, naturally followed.
Similarly, PLZT electrooptic modulator arrays of the type disclosed in the above mentioned 1972 Optoelectronics letter by Waterworth et al. have been considered suitable as the light modulating agency in a solid state oscillograph. In a similar vein, a PLZT device has been considered as an electrooptic shutter in an oscillograph of the Type 5-134 and the Type 5-139 manufactured by the subject assignee. In both types of recording oscillographs, light is emitted from a recording arc lamp through cylindrical belt lenses to be reflected by mirrors, one of which may be concave. In particular, in the Type 5-139, recording oscillograph, light is projected through belt lenses onto mirrors positioned at opposite sides of the arc lamp to be reflected onto a bank of galvanometer mirrors which, in turn, reflect the light back towards the general area of the lamp and beyond that lamp onto recording oscillograph paper through a collimating lens. To realize this construction, the path of the light is folded with the light-modulating elements, namely the galvanometer mirrors, forming a reflecting or folding agency in the light path.
In the Type 5-134 installation, part of the light generated by the recording arc lamp is emitted through a first cylindrical belt lens onto a mirror which, in turn, reflects such light onto a concave further mirror which reflects the light to a grid screen at the recording paper. This light path is folded by means of the mentioned mirrors, but neither any light-modulating or deflecting galvanometer mirror nor any light-modulating or gating PLZT or other solid state device is located in the light path.
In a modification contemplated for the above mentioned modified Type 5-134 installation a second part of the light is emitted by the arc lamp through a cylindrical belt lens, variable aperture and PLZT shutter to a mirror which reflects the light passed by the shutter to galvanometer mirrors through a galvanometer lens. The light modulated or deflected by the galvanometer mirrors is projected via a recording mirror and collimating lens onto advancing recording oscillograph paper. Again, a folded light path is utilized for these purposes, with the galvanometer mirrors forming a reflecting agency in the folded light path, in order to provide part thereof. Another folded light path in the Type 5-134 installation is provided for the light of a timing lamp which is located near the recording paper transport and emits light to a mirror located in the vicinity of the galvanometer mirrors and projecting light received from the timing lamp via the recording mirror and collimating lens onto the recording paper.
These installations, of course, still operated with conventional galvanometer mirrors, leaving unsatisfied the need for a solid state recording oscillograph using a PLZT or other type of solid state light gate structure. However, the prior art was notoriously unable to overcome various obstacles, entrenched prejudices and inadequacies which remained in the way of competitive solid state oscillograph and facsimile writing and reading equipment.
This will presently be explained with the aid of the above mentioned U.S. Pat. No. 3,930,119, by Schmidt et al., issued Dec. 30, 1975. It is to be pointed out in this connection that the problems presently to be discussed are endemic to the prior art and that the Schmidt patent has been selected as a convenient basis for discussion because of its symptomatic nature and relatively recent date.
One of the prevailing problems becomes apparent from a consideration of the fact that an effective light gating action requires each electrode or at least one electrode of each electrode pair to be individually connected to its own electric energizing wire. In this respect, several electrodes per millimeter have to be provided for adequate resolution. By way of example, Schmidt et al. mention an array of 1,200 lines of 800 picture elements each. At such high densities, the requisite individual terminal for each electrode becomes larger than the electrode itself, as may be seen from FIG. 12 on page 1871 of the above mentioned Cutchen article entitled PLZT Electrooptic Shutters: Applications. Accordingly, the inevitable minimum terminal size in practice is the limiting factor of electrode density and scanning or picture element resolution.
Another problem stems from the high light intensity required for solid state light gate operations and the very high light density required for oscillography papers, particularly those of the direct-print type required for real-time printout. While arc lamps and other high-indensity or point-type light sources exist, the problem becomes acute when an elongate light gate array is to be illuminated for selective light transmission. In this respect, the above mentioned Schmidt et al. patent proposes use of a tubular light source coextensive with the longest dimension of the light gate array and providing a uniform illumination thereacross. No existing light source having such elongate, coextensive configuration and meeting the applicable collimation and light-intensity requirements could be found.
In a similar vein, the well-known light scattering properties of PLZT and other solid state light gates, coupled with the natural diffraction imposed on light flowing through a multitude of narrow light gates, impose strict requirements, including collimation in two crossed directions to avoid sideways spread of the recording or illuminated reading point and to facilitate focusing of gated light to a small spot in the direction of travel of the recording medium or the master to be read.
Such bidirectional collimation appears lacking from the Schmidt et al. proposal. No remedy for this defect could be found in the remainder of the above mentioned references or any other existing or proposed system.
In particular, Swedish Pat. No. 47835, issued as of May 8, 1917 to Nordstrom et al., is representative of proposals employing a rotational-symmetrical concave reflector system for ideally issuing a cylindrical bundle of light. Such rotational-symmetrical light sources are not practically usable with elongate light gate structures of practical widths. Also, the text of the Swedish patent appears to imply that the light intensity achievable with such illumination systems may be rather non-uniform across the diameter of the cylindrical bundle of light. A drawback of the latter type is also apparent from U.S. Pat. No. 1,245,512, issued Nov. 6, 1917 to J. T. Roffy. That proposal employs several reflectors in the form of different figures of rotation in an attempt to convert the output of an incandescent lamp into a cylindrical beam of light. However, Roffy in effect teaches the provision of divergent light which travels along a center portion of a hollow-cylindrical light beam and which moreover permeates the otherwise collimated portion of that beam. This, of course, would be a completely unacceptable light source for light gate structures having the above mentioned inherent light scattering and diffraction properties.
More recent attemps at light sources of the type mentioned in the Swedish patent cited above may be seen in U.S. Pat. No. 3,796,886, issued Mar. 12, 1974, to M. L. Freeman, for Radiant Energy Reflectors, and U.S. Pat. No. 4,050,775, issued Sept. 27, 1977, to J. R. Scholten, for Catoptric Lens Arrangement. Those proposals also employ rotational-symmetrical reflector systems for generating hollow-cylindrical light beams and further utilize refractive means for providing an intensive beam of light along the longitudinal axis of the hollow-cylindrical light beam.
Again, such a non-uniform light emission renders those proposals unsuitable for light gate illumination or similar purposes. This applies also to the part of the cited Scholten reference which teaches the generation of divergent light bundles.
Rotational-symmetrical concave reflectors also have been employed in conjunction with convex reflectors in order to generate collimated beams of light. Such a system has been disclosed in U.S. Pat. No. 4,054,364, issued Oct. 18, 1977 to W. P. Webster, for Apparatus for Transmitting Light through Cassegrain Optics. As, however, shown in that patent, such a system also results in a hollow-cylindrical beam of light afflicted by a low light intensity along an axial space thereof.
Existing linear reflective devices would also be unsuitable for present purposes as may, for instance, be seen from U.S. Pat. No. 4,050,444, issued Sept. 27, 1977 to P. W. Dolamore, for Reflective Device. In addition to the fact that the Dolamore reflector system was designed for receiving, rather than issuing, radiation, there is the further fact that a light source substituted for any radiation receiver in the Dolamore system would in effect obstruct an essential part of the adjacent reflective surface.
That elongate light sources of the type proposed in the above mentioned Schmidt patent present no solution in practice may also be seen from Baxter, Document Illuminator Using Elliptic and Dichroic Reflectors, IBM Technical Disclosure Bulletin, Vol. 14, No. 11 (Apr. 1972). In particular, Baxter employs two elliptic-cylinder mirrors for focusing light from two parallel elongate lamps onto a narrow strip for photoelectric document reading purposes.
Such focused light is, however, neither collimated nor otherwise suitable for illumination of or use with elongate light gate structures.
Some prior proposals have employed folded light paths in illumination systems. For instance, Muirhead and McCallum have employed parabolic and plane mirror combinations in their Improvement in Spark Shadowgraph Technique, published in The Review of Scientic Instruments (Sept. 1959), pp. 830-831. Other folded light path systems have employed a laser as a more powerful light source than a spark gap.
In particular, folded light path systems have been employed to expand the relatively narrow beam emitted by practical lasers. However, this only provides for an expansion of the laser beam by a factor on the order of four, as may be seen from King, Unobstructed Laser-Beam-Expander Pointing System with Tilted Spherical Mirrors, published in Applied Optics (Jan. 1974) p. 21. No solution to this or any of the above mentioned problems is apparent from the laser beam expanding system disclosed in U.S. Pat. No. 3,531,205, by T. A. Nussmeier, issued Sept. 29, 1970, for Light Beam Aiming Device, or from the folded light path system of U.S. Pat. No. 3,871,773, by H. E. Shaw, issued Mar. 18, 1975.
Prior systems using a partially transparent curved rotational-symmetrical reflecting surface and crossed polarizers in infinite optical image-forming apparatus, such as disclosed in U.S. Pat. No. 3,443,858, by J. La Russa, issued May 13, 1969, would be too inefficient in practice and would otherwise be unsuitable for illuminating elongate light gate structures and similar apparatus.
In consequence, prior practical electrooptical devices have remained limited to the relatively small size apparent from U.S. Pat. Nos. 2,649,027, 2,909,972 and 3,020,805.
The facts herein recited and the lack of suitable proposals in the prior art underscore the reason for the entrenched dominance of the field of oscillography by the electromechanical galvanometer for many decades. The prior-art climate in this respect appears to be well reflected in the above mentioned Zook reference which compares the electromechanical galvanometer oscillograph with modern developments including electrooptic and acoustooptic light beam deflectors and which recognizes that the electromechanical galvanometer provides the lowest access time (i.e. the slowest response) in terms of both present and projected performance. Despite this expressly confirmed drawback, Zook concludes on page 875 that "it has become clear that, whenever possible, mechanical deflectors are preferable," thereby in effect putting a damper on further developments in the solid-state galvanometer area.
While emphasis has been placed on oscillography in this disclosure statement, it should be understood that the subject invention has utility in other areas, such as those suggested by or apparent from the description of preferred embodiments or by the language of the claims.